JP4304913B2

JP4304913B2 - How to repair cracked defects

Info

Publication number: JP4304913B2
Application number: JP2002114094A
Authority: JP
Inventors: 克仁高橋; 武志塚本; 満夫中村
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2002-04-17
Filing date: 2002-04-17
Publication date: 2009-07-29
Anticipated expiration: 2022-04-17
Also published as: JP2003311463A

Description

【０００１】
【発明の属する技術分野】
本発明は亀裂状の欠陥が発生した構造物の補修方法に係わり、特に亀裂状の欠陥の内部に水，酸化物等の介在物を含む金属材料に対して、雰囲気中の酸素分圧を制御した雰囲気下で肉盛溶接または表面溶融処理することにより、亀裂状の欠陥を封止し、前記亀裂状欠陥内部の更なる腐食や亀裂状欠陥の成長を防ぐ技術に関する。本発明は水中構造物や原子炉炉内機器の亀裂状欠陥の補修に好適である。
【０００２】
【従来の技術】
従来、亀裂状の欠陥が発生した原子炉炉内機器の補修方法として、亀裂状の欠陥が発生した部分を、溶融層で被覆したり、補修板材で被覆したりしてそれを溶接する補修方法（特開平８−２９５８０号公報）や、金属材料に含まれるヘリウム量に応じて入熱量を制御しながら、肉盛層で被覆する補修方法（特開２０００−２３０９９６号公報）が知られているが、亀裂状の欠陥の内部に水，酸化物等の介在物が欠陥封止性に及ぼす影響については触れられていない。
【０００３】
また、亀裂状の欠陥内に介在物を含む欠陥部の補修方法（特開２００１−２４２２８０号公報，特開２００１−２８７０６２号公報）が知られているが、これらは酸化物等の介在物を積極的に加熱して解離させるか、介在物を溶融除去するなどしてから肉盛溶接を施す補修方法である。
【０００４】
これらの公知例を含む従来の溶接や表面溶融処理は、補修部の酸化を防ぐために、不活性ガスの雰囲気下や還元性を有するガスの雰囲気下で行われる。
【０００５】
また、不活性ガスであるアルゴンと活性ガスである酸素の混合ガスを雰囲気に用いる補修溶接法（特開平１１−２８５６５号公報，特開２００１−７１１３５号公報）が知られている。特開平１１−２８５６５号公報に記載の方法は、大気圧より圧力の高い雰囲気下で溶接を行う場合に適用され、酸素との反応による溶接金属中のマンガンの損失を低減するために、不活性ガスの分圧を調整して、活性ガスの分圧を大気圧での分圧と等しくなるようにするものである。
【０００６】
特開２００１−７１１３５号公報に記載の方法はアーク溶接の電極用ワイヤやワークの材質により変化する溶接条件に合わせるためのものである。
【０００７】
【発明が解決しようとする課題】
亀裂状欠陥の補修において、亀裂状欠陥内に水，酸化物等の介在物が含まれる場合には、溶接時の加熱により介在物が変化し、反応生成物が溶融池で噴出し、欠陥部を完全に被覆できないことが特開２００１−２４２２８０号公報により指摘されている。
【０００８】
本発明者らも、内部に水，酸化物等の介在物を大量に含む亀裂状欠陥が発生した構造物の表面を、単に肉盛層を繰返しラップさせて、表面を肉盛層で被覆する補修方法では、水，酸化物からの反応生成物によると推定される噴出しが溶融池において起こり、完全に封止できない場合があることを確認した。
【０００９】
本発明は、亀裂状欠陥の内部に介在物、特に水，酸化物を含む場合に、不活性ガスに混合する酸素の分圧を制御することにより、水，酸化物等の介在物からの反応生成物の発生を抑制し、亀裂状の欠陥を生じた部分を介在物ごと肉盛溶接して封止し、亀裂状欠陥の内部に更なる腐食が生じたりあるいは亀裂状欠陥が成長するのを防ぐ補修方法を提供するものである。
【００１０】
本発明は、耐食性が低下した金属材料に対して、耐食性を向上させるための表面溶融処理に適用することができ、亀裂内部の介在物、特に水，酸化物が原因となる溶融部におけるガスの噴出しを低減した補修方法を提供できる。
【００１１】
【課題を解決するための手段】
本発明は、以下のとおりである。
（１）構造物の表面に発生した、内部に水，酸化物等の介在物を含む亀裂状欠陥を、レーザを溶接熱源とし、肉盛溶接により形成した肉盛金属で表面を被覆する補修方法において、不活性ガスに混合する酸素の分圧を制御した雰囲気下で、前記亀裂状欠陥が発生した部分を前記肉盛金属で被覆することを特徴とする。
（２）構造物の表面に発生した、内部に水，酸化物等の介在物を含む亀裂状欠陥がある領域を、レーザを溶接熱源とし、表面溶融処理により形成した溶融凝固層で表面を被覆する補修方法において、不活性ガスに混合する酸素の分圧を制御した雰囲気下で、前記亀裂状欠陥が発生した部分を前記溶融凝固層で被覆することを特徴とする。
（３）先の（１）または（２）の発明において、前記酸素分圧は、溶接入熱量に応じて制御することを特徴とする。
（４）先の（１）または（２）の発明において、前記溶接入熱量は亀裂状欠陥の開口幅が最も広いところを基準にして決定することを特徴とする。
（５）先の（１）または（２）の発明において、前記酸素分圧は、前記介在物の種類に応じて制御することを特徴とする。
（６）先の発明において、前記補修を水中環境下にて、欠陥部の水を局所的に排除しながら行うことを特徴としている。
（７）先の発明において、不活性ガスに酸素を混合した雰囲気下での被覆を多層に重ねることを特徴とする。
（８）先の発明において、不活性ガスに酸素を混合した雰囲気下で被覆を行い、前記被覆を施した部分を覆うように、複数回、不活性ガス雰囲気下または還元性を有する雰囲気下で被覆することを特徴とする。
（９）先の発明において、不活性ガス雰囲気下または還元性を有する雰囲気下での複数回重ねる被覆は、不活性ガスに酸素を混合した雰囲気下での被覆よりも溶接入熱量または溶融入熱量を小さくして行うことを特徴とする。
【００１２】
【発明の実施の形態】
本発明は亀裂状欠陥の補修に関して、不活性ガスに添加する酸素の分圧を制御した雰囲気下で溶接を行うことにあり、酸素の分圧は溶接入熱量や亀裂状欠陥内に含まれる介在物の種類によって決定される。
【００１３】
原子炉炉内機器を構成する金属材料は主に低合金鋼やステンレス鋼等の鉄基合金，ニッケル基合金である。本発明はこれらの金属材料のような構造物に対して適用可能である。以下、実施例に基づいて詳細に説明する。
【００１４】
〔第１実施例〕
図１により、原子炉内機器の補修方法および補修装置について説明する。原子炉炉内機器を構成する金属材料１０１には応力腐食割れにより亀裂状欠陥１０２が発生している。金属材料１０１は、ステンレス鋼等の鉄基合金、または、
Alloy600（インコネル社の商標）等のニッケル基合金であり、亀裂状欠陥１０２は、内部に水，酸化物等の介在物を含んでいる。
【００１５】
Ｎｄ：ＹＡＧレーザ発振器２０１から発せられたレーザ光２０２を、光ファイバー２０３または導光管を介してトーチ２０４へ導く。トーチ２０４先端に装着したノズル２０５より不活性ガスと酸素とが混合した不活性ガス・酸素混合ガス２０６を噴出する。ここで、不活性ガスとはヘリウム，アルゴン等の希ガス，窒素である。レーザ光２０２を照射することにより形成される溶融池にフィラーワイヤ２０７を供給しながら、トーチ２０４を金属材料１０１に対し移動させて肉盛金属１０３を形成する。監視や非破壊検査等により欠陥開口部の幅を求め、開口幅から溶接入熱量を決定する。溶接入熱量はレーザの出力やトーチ２０４の移動速度を変えることによって調整する。フィラーワイヤ２０７の材質については、金属材料１０１と同じ成分のもの、金属材料１０１よりも耐食性に優れているものを用いると良い。
【００１６】
さらに、肉盛金属１０３をラップさせながら、亀裂が発生した欠陥部分を肉盛金属で被覆する。肉盛層と肉盛層とが重なり合う割合は、ビード幅の１／４〜１／２すると良い。
【００１７】
内部に水，酸化物等の介在物を含まない場合、溶接入熱量が大きい程、亀裂状欠陥は封止しやすい。本発明者らは実験により、最低でも０.６ｋＪ／cm の溶接入熱量があれば、開口幅０.７mm の亀裂状欠陥を封止できることを明らかにした。
【００１８】
しかし、内部に水，酸化物等の介在物を含まない場合には封止可能であっても、内部に水，酸化物を含む場合では、補修部に不具合を生じてしまい、うまく封止することができないことがある。
【００１９】
そこで、本発明では内部に水，酸化物を含む亀裂状欠陥に対しては、不活性ガスに酸素を添加した雰囲気において補修を行う。
【００２０】
酸素分圧を制御した雰囲気において補修することにより、補修部における不具合が低減される理由について、鉄系酸化物のＦｅ₃Ｏ₄，ＦｅＯを例に説明する。酸化物生成自由エネルギー温度酸素圧線図を図２に示す。縦軸は酸化物の生成自由エネルギー、横軸は温度を表しており、図中の太い実線は酸化還元反応６FeO＋Ｏ₂＝２Ｆｅ₃Ｏ₄ の平衡状態を、点線は各酸素分圧における酸素圧線を表している。（大気圧下での酸素含有量に換算して表した。）
大気圧下で、四酸化三鉄（Ｆｅ₃Ｏ₄）を加熱した場合において、市販されている普通純度のアルゴンガスは０.００１パーセント程度の酸素を含有している。この場合、酸素分圧は１×１０^-5atm であるから、１８５０Ｋ付近から酸化物の解離が起こる。
【００２１】
一方で不活性ガスに酸素が体積比で２０パーセント混合した雰囲気下ではおよそ２３５０Ｋにならないと酸化物の解離は起こらないことになる。
【００２２】
本発明者らは、雰囲気中の酸素含有量を系統的に変化させ、内部にＦｅ₃Ｏ₄を含む開口幅０.５mmの亀裂状の欠陥に対して、溶接入熱量を０.６ｋＪ／cmにして肉盛溶接を行った。
【００２３】
酸素の分圧が０.０１atmの雰囲気下では、補修部に不具合が発生したが、酸素分圧が０.２atmの雰囲気下では、補修部における反応生成物の噴出しが抑えられた。
【００２４】
また、Ｆｅ₂Ｏ₃よりも解離し易いとされるＦｅ₃Ｏ₄，ＮｉＯを内部に含む亀裂状欠陥についても同様の結果が得られ、封止が可能であることを確認した。
【００２５】
介在物が加熱される温度が分かれば、不活性ガス・酸素混合ガス中の酸素の分圧を、図２より決定することができる。
【００２６】
しかし、実際に介在物が加熱される温度を求めることは困難である。
【００２７】
また、加熱される温度が求まったとして、図２より酸素分圧を決定しても、混合ガス中の酸素が溶融金属との反応に費やされ、実際に酸化物に到達する混合ガスの酸素分圧が低下してしまい、効果が得られないことも考えられる。
【００２８】
さらに、実際の亀裂状欠陥の内部に含まれる酸化物は鉄系の酸化物，ニッケル系の酸化物，クロム系の酸化物、それらの複合酸化物が考えられ、想定される酸化物の種類により解離特性が異なり、それに従い、適切な酸素分圧も変化する。
【００２９】
そこで、予測される状況を模擬した試験を行い、試験結果から溶接入熱量に応じて酸素分圧を決定すると良い。
【００３０】
さらに、補修対象箇所のサンプリング等により、介在物の種類を予め同定しておいて、それに応じて酸素分圧を決定するとなお良い。
【００３１】
肉盛層が１層だけでは亀裂状欠陥を封止できなかった場合、または、肉盛層が１層だけでは耐久性に乏しい場合には、図３に示すように肉盛層を多層に積み重ねる。
【００３２】
本発明を適用する亀裂状の欠陥が発生した部分は必ずしも平坦である必要はなく、円筒の内側の曲面に対してや、放電加工や切削によっても亀裂状の欠陥を完全に除去しきれなかった凹部に対して適用しても良い。
【００３３】
酸素が混合した雰囲気下で肉盛溶接を行うと、肉盛金属１０３の表面は酸化してしまう。そこで図４に示すように、肉盛金属１０３を不活性ガス、または還元性を有する雰囲気下で肉盛溶接して被覆することによって、表面の酸化が少ない肉盛金属１０４を得ることができる。不活性ガス、または還元性を有する雰囲気下での肉盛溶接を行う場合、肉盛金属で封止された前記欠陥内の介在物を再び加熱してしまうことがないように、不活性ガス、または還元性を有する雰囲気下での肉盛溶接の溶接入熱量は小さくした方が良い。肉盛金属を形成するパスごとに雰囲気を変えるのではなく、パスの途中で雰囲気を変えても良い。
【００３４】
〔第２実施例〕
本発明を水中で適用する実施例を説明する。加工部との間のレーザの光路および加工部周辺の領域の水を排除することにより、水中にて本発明を行う。実際には、亀裂状欠陥内部の水を完全に排除することは難しく、亀裂状欠陥のある金属材料表面に水が残っていると、肉盛金属の溶着が妨げられ、〔第１実施例〕にくらべて溶接条件の範囲が狭くなってしまう。それを低減するために溶接入熱量を大きくして積極的に水分を蒸発させることができるが、一方で、欠陥内部の介在物を加熱してしまうことになり、酸化物の解離や欠陥内部での水蒸気の発生を促進してしまい、溶融部での噴出しを活発にすることになる。そこで、噴出しの原因となる介在物の反応を抑えるために、不活性ガスに酸素を添加した雰囲気にて補修を行う。
【００３５】
まず、水中補修装置の一例を示す。図５のように不活性ガスと酸素との混合ガス２０８をノズル２０５先端より噴射して、水を排除する。それと同時に噴射口と加工部周辺との間に形成した気相空間を不活性ガスと酸素との混合ガス雰囲気とすることができる。
【００３６】
そして、第１実施例と同様にＮｄ：ＹＡＧ等のレーザ発振器２０１から発せられたレーザ光２０２を導光管、または光ファイバー２０３を介してトーチへ導く。さらに、レーザ光２０２の光軸と金属材料１０１の交点近傍にフィラーワイヤ２０７を供給しながら、トーチ２０４を金属材料１０１に対し移動させて肉盛金属１０３を形成する。溶接入熱量は、監視により欠陥開口部の幅から決定し、レーザの出力やトーチ２０４の移動速度を変えることによって調整する。フィラーワイヤ２０７の材質については、金属材料１０１と同じ成分のもの、金属材料１０１よりも耐食性に優れているものを用いると良い。
【００３７】
さらに、肉盛金属１０３をラップさせながら、亀裂が発生した欠陥部分を肉盛金属で被覆する。ビードとビードとが重なり合う割合は、ビード幅の１／４〜１／２にすると良い。
【００３８】
水の排除方法については、必ずしもノズル先端より噴出させるガスによって水を排除するものでなくても良く、レーザの光路および溶接部の水を排除することができる方法であれば良い。具体的な水の排除方法として、例えば、固体隔壁方式や水カーテン方式がある。
【００３９】
〔第３実施例〕
オーステナイト系ステンレス鋼の経年変化として、応力腐食割れが重要な問題となっている。
【００４０】
オーステナイト系ステンレス鋼の溶接部近傍等の熱影響を受けた領域では、構成元素であるクロムと、不純物として含まれる炭素とが粒界近傍でクロム炭化物を形成することによりクロムが粒界で欠乏し、粒界の耐食性が低下する現象が発生する。この様な材料の変化を、ここでは鋭敏化ということにする。鋭敏化した材料に、外部からの応力や溶接による残留応力が加わり、さらに、酸素，塩素などの有害な物質が含まる環境に曝されることにより、応力腐食割れが発生する。
【００４１】
応力腐食割れは、材料因子，応力因子，環境因子の３つの因子が相乗的に寄与することにより発生するとされており、応力腐食割れ防止法として、３因子のうちのいずれかを改良する方法がとられている。
【００４２】
材料因子である材料鋭敏化対策の１つとして、材料をある温度に一定時間保持するか溶融して、クロムや炭素を均一に固溶させた後、急冷する表面改質処理がとられる。そこで本発明を、鋭敏化が発生し、さらに、内部に酸化物等の介在物を含む亀裂状欠陥がある部分を溶融して、表面改質処理する補修方法に適用し、その実施例について説明する。鋭敏化した金属材料１０５で、さらに、内部に酸化物等の介在物を含む亀裂状欠陥１０２がある部分を溶融して、溶融層で金属材料を被覆する実施例について説明する。まず、不活性ガスと酸素が混合した雰囲気下で表面溶融処理を行うことによって亀裂状欠陥１０２ごと溶融してしまうか、前記欠陥１０２を溶融凝固層１０６で封止する。このままでは、表面が酸化したままなので、表面が酸化した溶融凝固層に重ねて不活性ガス雰囲気下または還元性を有する雰囲気下で溶融処理すると良い。酸化層が還元されることにより、表面の酸化が少ない溶融凝固層を得ることができる。後者の処理を行う場合、溶融凝固層で封止された前記欠陥内の介在物を再び加熱してしまうと溶融凝固層に不具合を生じるから、後者の表面溶融処理の入熱量は小さくした方が良い。入熱量を減らせば、溶融凝固層の幅は小さくなると予想されるから、間隔を減らすと良い。溶融凝固層と溶融凝固層とが重なり合う割合は、溶融凝固層の１／４〜１／２にすると良い。〔第３実施例〕の方法は金属材料が鋭敏化していなくても、内部に酸化物等の介在物を含む亀裂状欠陥を溶融して封止する場合に実施しても良い。また、鋭敏化した金属材料１０５の表面に肉盛溶接をしても良い。
【００４３】
【発明の効果】
本発明を補修作業に適用すれば、構造物の亀裂状欠陥が発生した金属材料に対して、更なる亀裂内部の腐食や亀裂の成長を阻止することが可能である。本発明は、原子炉の長寿命化，予防保全に効果がある。また、水中環境下で行えば、補修作業を効率的に行うことができ、作業員の安全に有効である。
【図面の簡単な説明】
【図１】第１実施例の補修方法に関して、補修装置と本発明を適用した施工方法を説明するために、施工方向に平行な面から見た断面図。
【図２】酸化物の生成自由エネルギー温度−酸素圧線図。
【図３】第１実施例の補修方法に関して、多層に肉盛する場合の肉盛溶接の施工方法を説明するために、施工方向に垂直な面から見た断面図。
【図４】第１実施例の補修方法に関して、雰囲気を変えて肉盛する場合の肉盛溶接の施工方法を説明するために、施工方向に垂直な面から見た断面図。
【図５】第２実施例の補修方法に関して、水中における、補修装置と本発明を適用した施工方法を説明するために、施工方向に平行な面から見た断面図。
【図６】第３実施例の補修方法に関して、鋭敏化した金属材料を表面溶融して耐食性を改善する施工方法を説明するために、施工方向に垂直な面から見た断面図。
【符号の説明】
１０１…金属材料、１０２…亀裂状欠陥、１０３，１０４…肉盛金属、１０５…鋭敏化した金属材料、１０６…溶融凝固層、２０１…レーザ発振器、２０２…レーザ光、２０３…光ファイバー、２０４…トーチ、２０５…ノズル、２０６…不活性ガス・酸素混合ガス、２０７…フィラーワイヤ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for repairing a structure in which a crack-like defect has occurred, and in particular controls the oxygen partial pressure in the atmosphere for a metal material containing inclusions such as water and oxide inside the crack-like defect. The present invention relates to a technique for sealing a crack-like defect by performing overlay welding or surface melting treatment in an atmosphere, and preventing further corrosion inside the crack-like defect and growth of the crack-like defect. The present invention is suitable for repairing crack-like defects in underwater structures and in-reactor equipment.
[0002]
[Prior art]
Conventionally, as a repair method for in-reactor equipment in which crack-like defects have occurred, a repair method in which the part where crack-like defects have occurred is covered with a molten layer or covered with a repair plate and welded. (Japanese Patent Laid-Open No. 8-29580) and a repair method (Japanese Patent Laid-Open No. 2000-230996) for covering with a built-up layer while controlling the amount of heat input according to the amount of helium contained in the metal material are known. However, there is no mention of the influence of inclusions such as water and oxides on the defect sealing properties inside the crack-like defects.
[0003]
Further, methods for repairing a defect portion including inclusions in crack-like defects (Japanese Patent Laid-Open Nos. 2001-242280 and 2001-287062) are known, but these include inclusions such as oxides. This is a repair method in which overlay welding is performed after positively heating to dissociate or melting and removing inclusions.
[0004]
Conventional welding and surface melting treatments including these known examples are performed in an inert gas atmosphere or a reducing gas atmosphere in order to prevent oxidation of the repaired portion.
[0005]
Further, there is known a repair welding method (JP 11-28565 A, JP 2001-71135 A) using a mixed gas of argon as an inert gas and oxygen as an active gas in an atmosphere. The method described in JP-A-11-28565 is applied when welding is performed in an atmosphere at a pressure higher than atmospheric pressure, and is inert to reduce the loss of manganese in the weld metal due to the reaction with oxygen. The partial pressure of the gas is adjusted so that the partial pressure of the active gas becomes equal to the partial pressure at atmospheric pressure.
[0006]
The method described in Japanese Patent Laid-Open No. 2001-71135 is for adjusting to welding conditions that vary depending on the material of the electrode wire or workpiece for arc welding.
[0007]
[Problems to be solved by the invention]
In repairing crack-like defects, when inclusions such as water and oxides are included in the crack-like defects, the inclusions change due to heating during welding, and the reaction product is ejected from the molten pool, resulting in defective parts. JP-A-2001-242280 points out that the film cannot be completely covered.
[0008]
The inventors of the present invention also cover the surface of the structure in which crack-like defects including a large amount of inclusions such as water and oxide are generated by simply wrapping the overlay layer and covering the surface with the overlay layer. In the repair method, it was confirmed that there was a case in which ejection that was estimated to be caused by reaction products from water and oxide occurred in the molten pool and could not be completely sealed.
[0009]
The present invention provides a reaction from inclusions such as water and oxides by controlling the partial pressure of oxygen mixed with an inert gas when inclusions, particularly water and oxides, are contained inside crack-like defects. Suppress the generation of the product, seal the welded part together with the inclusions, and prevent further corrosion inside the cracked defect or growth of the cracked defect. It provides repair methods to prevent.
[0010]
The present invention can be applied to the surface melting treatment for improving the corrosion resistance of the metal material having reduced corrosion resistance, and the gas in the molten portion caused by inclusions inside the crack, particularly water and oxides. A repair method with reduced ejection can be provided.
[0011]
[Means for Solving the Problems]
The present invention is as follows.
(1) A repair method of covering a surface of a crack-like defect generated on the surface of a structure including inclusions such as water and oxide with a built-up metal formed by overlay welding using a laser as a welding heat source. In the above, in the atmosphere in which the partial pressure of oxygen mixed with the inert gas is controlled, the portion where the crack-like defect has occurred is covered with the overlay metal.
(2) Cover the surface of the structure that has cracked defects that contain inclusions such as water and oxide inside with a melt-solidified layer formed by surface melting treatment using laser as a welding heat source. The repairing method is characterized in that a portion where the crack-like defect has occurred is covered with the molten solidified layer in an atmosphere in which the partial pressure of oxygen mixed with the inert gas is controlled.
(3) In the above invention (1) or (2), the oxygen partial pressure is controlled in accordance with a welding heat input.
(4) In the invention of the above (1) or (2), the amount of welding heat input is determined on the basis of a place where the opening width of the crack-like defect is widest.
(5) In the above invention (1) or (2), the oxygen partial pressure is controlled according to the type of the inclusion.
(6) In the above invention, the repair is performed in an underwater environment while locally removing the water in the defective portion.
(7) In the above invention, the coating in an atmosphere in which an inert gas is mixed with oxygen is stacked in multiple layers.
(8) In the previous invention, the coating is performed in an atmosphere in which oxygen is mixed with an inert gas, and a plurality of times in an inert gas atmosphere or a reducing atmosphere so as to cover the coated portion. It is characterized by covering.
(9) In the previous invention, the coating that is stacked a plurality of times in an inert gas atmosphere or in an atmosphere having a reducing property is greater in the amount of welding heat input or the melting heat input than the coating in an atmosphere in which an inert gas is mixed with oxygen. It is characterized in that it is performed with a small value.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to repair of crack-like defects in that welding is performed in an atmosphere in which the partial pressure of oxygen added to the inert gas is controlled. The partial pressure of oxygen is included in the amount of welding heat input and crack-like defects. Determined by the type of object.
[0013]
The metal materials constituting the reactor internal equipment are mainly iron-base alloys and nickel-base alloys such as low alloy steel and stainless steel. The present invention is applicable to structures such as these metal materials. Hereinafter, it demonstrates in detail based on an Example.
[0014]
[First embodiment]
With reference to FIG. 1, a repair method and a repair device for in-reactor equipment will be described. A crack-like defect 102 is generated by stress corrosion cracking in the metal material 101 constituting the in-reactor equipment. The metal material 101 is an iron-based alloy such as stainless steel, or
It is a nickel-based alloy such as Alloy 600 (trademark of Inconel), and the crack-like defect 102 contains inclusions such as water and oxide inside.
[0015]
The laser beam 202 emitted from the Nd: YAG laser oscillator 201 is guided to the torch 204 through the optical fiber 203 or the light guide tube. An inert gas / oxygen mixed gas 206 in which an inert gas and oxygen are mixed is ejected from a nozzle 205 attached to the tip of the torch 204. Here, the inert gas is a rare gas such as helium or argon, or nitrogen. While supplying the filler wire 207 to the molten pool formed by irradiating the laser beam 202, the torch 204 is moved relative to the metal material 101 to form the overlay metal 103. The width of the defect opening is obtained by monitoring, nondestructive inspection, etc., and the welding heat input is determined from the opening width. The welding heat input is adjusted by changing the laser output and the moving speed of the torch 204. As for the material of the filler wire 207, a material having the same component as the metal material 101 or a material having better corrosion resistance than the metal material 101 may be used.
[0016]
Furthermore, while the built-up metal 103 is wrapped, the defect portion where the crack has occurred is covered with the built-up metal. The ratio at which the overlay layer and the overlay layer overlap is preferably 1/4 to 1/2 of the bead width.
[0017]
When inclusions such as water and oxides are not included inside, the larger the welding heat input, the easier it is to seal crack-like defects. Through experiments, the present inventors have shown that a crack-like defect having an opening width of 0.7 mm can be sealed with a minimum amount of welding heat input of 0.6 kJ / cm 2.
[0018]
However, even if it can be sealed if it does not contain inclusions such as water and oxide, if it contains water and oxide, it will cause a defect in the repaired part and seal well. There are times when you can't.
[0019]
Therefore, in the present invention, crack-like defects containing water and oxide are repaired in an atmosphere in which oxygen is added to an inert gas.
[0020]
The reason why defects in the repaired part are reduced by repairing in an atmosphere in which the oxygen partial pressure is controlled will be described by taking Fe ₃ O ₄ and FeO of iron-based oxides as an example. The oxide formation free energy temperature oxygen pressure diagram is shown in FIG. The vertical axis represents the free energy of formation of the oxide, the horizontal axis represents the temperature, the thick solid line in the figure represents the equilibrium state of the oxidation-reduction reaction 6FeO + O ₂ = 2Fe ₃ O ₄ , and the dotted line represents the oxygen pressure line at each oxygen partial pressure. Represents. (Expressed in terms of oxygen content at atmospheric pressure)
When triiron tetroxide (Fe ₃ O ₄ ) is heated under atmospheric pressure, commercially available normal-purity argon gas contains about 0.001 percent oxygen. In this case, since the oxygen partial pressure is 1 × 10 ⁻⁵ atm, the oxide dissociates from around 1850K.
[0021]
On the other hand, in an atmosphere where oxygen is mixed with an inert gas at a volume ratio of 20%, dissociation of the oxide does not occur unless the temperature is about 2350K.
[0022]
The present inventors systematically change the oxygen content in the atmosphere, and with respect to a crack-like defect having an opening width of 0.5 mm containing Fe ₃ O ₄ therein, the welding heat input is 0.6 kJ / cm. Then, overlay welding was performed.
[0023]
In the atmosphere where the partial pressure of oxygen was 0.01 atm, trouble occurred in the repaired part, but in the atmosphere where the oxygen partial pressure was 0.2 atm, the ejection of reaction products in the repaired part was suppressed.
[0024]
Similar results were obtained for cracked defects containing Fe ₃ O ₄ and NiO, which are considered to be more easily dissociated than Fe ₂ O _3, and it was confirmed that sealing was possible.
[0025]
If the temperature at which the inclusions are heated is known, the partial pressure of oxygen in the inert gas / oxygen mixed gas can be determined from FIG.
[0026]
However, it is difficult to determine the temperature at which inclusions are actually heated.
[0027]
Further, assuming that the temperature to be heated is obtained, even if the oxygen partial pressure is determined from FIG. 2, oxygen in the mixed gas is consumed in the reaction with the molten metal, and the oxygen in the mixed gas that actually reaches the oxide It is conceivable that the partial pressure is lowered and the effect cannot be obtained.
[0028]
In addition, the oxides contained in the actual crack-like defects may be iron-based oxides, nickel-based oxides, chromium-based oxides, and complex oxides of these, depending on the type of oxides that are assumed. The dissociation characteristics are different and the appropriate oxygen partial pressure changes accordingly.
[0029]
Therefore, it is preferable to conduct a test simulating the predicted situation and determine the oxygen partial pressure from the test result according to the welding heat input.
[0030]
Furthermore, it is more preferable that the type of inclusion is identified in advance by sampling the repair target location and the oxygen partial pressure is determined accordingly.
[0031]
When it is not possible to seal crack-like defects with only one overlay layer, or when durability is insufficient with only one overlay layer, the overlay layers are stacked in multiple layers as shown in FIG. .
[0032]
The portion where the crack-like defect is applied is not necessarily flat to which the present invention is applied, and the concave portion where the crack-like defect could not be completely removed with respect to the curved surface inside the cylinder, or by electric discharge machining or cutting. You may apply to.
[0033]
When overlay welding is performed in an atmosphere in which oxygen is mixed, the surface of the overlay metal 103 is oxidized. Therefore, as shown in FIG. 4, the cladding metal 104 with less surface oxidation can be obtained by covering the cladding metal 103 by depositing the cladding in an inert gas or a reducing atmosphere. Inert gas or when performing overlaying welding in an atmosphere which is reducing, so as not to cause heating the inclusions in said defect sealed with cladding metal again, an inert gas, Or it is better to make the welding heat input of overlay welding under an atmosphere having a reducing property small. Instead of changing the atmosphere for each pass forming the overlay metal, the atmosphere may be changed in the middle of the pass.
[0034]
[Second Embodiment]
An embodiment in which the present invention is applied in water will be described. The present invention is performed in water by eliminating the optical path of the laser with the processing section and the water in the area around the processing section. Actually, it is difficult to completely eliminate the water inside the crack-like defect, and if water remains on the surface of the metal material having the crack-like defect, the welding of the build-up metal is hindered, [First Example] Compared to this, the range of welding conditions becomes narrower. In order to reduce this, it is possible to actively evaporate moisture by increasing the welding heat input, but on the other hand, the inclusions inside the defect will be heated, and the oxide dissociation and inside the defect The generation of water vapor is promoted, and the ejection at the melting part is activated. Therefore, in order to suppress the reaction of inclusions that cause ejection, repair is performed in an atmosphere in which oxygen is added to an inert gas.
[0035]
First, an example of the underwater repair device is shown. As shown in FIG. 5, a mixed gas 208 of an inert gas and oxygen is injected from the tip of the nozzle 205 to remove water. At the same time, the gas phase space formed between the injection port and the periphery of the processed portion can be a mixed gas atmosphere of an inert gas and oxygen.
[0036]
As in the first embodiment, the laser beam 202 emitted from the laser oscillator 201 such as Nd: YAG is guided to the torch via the light guide tube or the optical fiber 203. Furthermore, while supplying the filler wire 207 near the intersection of the optical axis of the laser beam 202 and the metal material 101, the torch 204 is moved relative to the metal material 101 to form the overlay metal 103. The welding heat input is determined from the width of the defect opening by monitoring and is adjusted by changing the laser output and the moving speed of the torch 204. As for the material of the filler wire 207, a material having the same component as the metal material 101 or a material having better corrosion resistance than the metal material 101 may be used.
[0037]
Furthermore, while the built-up metal 103 is wrapped, the defect portion where the crack has occurred is covered with the built-up metal. The ratio of the bead and the bead is preferably set to 1/4 to 1/2 of the bead width.
[0038]
The method for removing water does not necessarily have to be eliminated by the gas ejected from the nozzle tip, and any method can be used as long as it can eliminate the laser light path and the water in the weld. Specific methods for removing water include, for example, a solid partition system and a water curtain system.
[0039]
[Third embodiment]
Stress corrosion cracking has become an important issue as the secular change of austenitic stainless steel.
[0040]
In areas affected by heat, such as near the weld zone of austenitic stainless steel, chromium, which is a constituent element, and carbon contained as an impurity form chromium carbide near the grain boundary, so that chromium is deficient at the grain boundary. The phenomenon that the corrosion resistance of the grain boundary is lowered occurs. This material change is called sensitization here. Stress corrosion cracking occurs when the sensitized material is subjected to external stress or residual stress due to welding, and is exposed to an environment containing harmful substances such as oxygen and chlorine.
[0041]
Stress corrosion cracking is caused by the synergistic contribution of three factors: material factor, stress factor, and environmental factor. As a stress corrosion cracking prevention method, there is a method for improving any one of the three factors. It has been taken.
[0042]
As one of countermeasures for material sensitization, which is a material factor, surface modification treatment is performed in which a material is kept at a certain temperature for a certain period of time or melted to uniformly dissolve chromium and carbon, and then rapidly cooled. Therefore, the present invention is applied to a repair method in which sensitization occurs and a portion having crack-like defects including inclusions such as oxides in the interior is melted and surface-modified, and an example thereof is described. To do. An example will be described in which a portion having a crack-like defect 102 including inclusions such as oxides is melted in the sensitized metal material 105 and the metal material is covered with a molten layer. First, by performing a surface melting treatment in an atmosphere in which an inert gas and oxygen are mixed, the crack-like defect 102 is melted or the defect 102 is sealed with a molten solidified layer 106. In this state, since the surface remains oxidized, it is preferable to carry out the melting treatment in an inert gas atmosphere or an atmosphere having a reducing property on the melt-solidified layer whose surface is oxidized. By reducing the oxide layer, a melt-solidified layer with less surface oxidation can be obtained. When the latter treatment is performed, if the inclusions in the defect sealed with the melt-solidified layer are heated again, a defect occurs in the melt-solidified layer. Therefore, the heat input amount of the latter surface melting treatment should be reduced. good. If the amount of heat input is reduced, the width of the melt-solidified layer is expected to be reduced. The overlapping ratio of the melt-solidified layer and the melt-solidified layer is preferably 1/4 to 1/2 of the melt-solidified layer. The method of [Third Embodiment] may be carried out when a cracked defect containing inclusions such as oxide is melted and sealed, even if the metal material is not sensitized. Further, overlay welding may be performed on the surface of the sensitized metal material 105.
[0043]
【The invention's effect】
If the present invention is applied to repair work, it is possible to prevent further corrosion inside the crack and growth of cracks in the metal material in which the crack-like defect of the structure has occurred. The present invention is effective for extending the life of a nuclear reactor and for preventive maintenance. Moreover, if it is performed in an underwater environment, the repair work can be performed efficiently, which is effective for the safety of workers.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view seen from a plane parallel to a construction direction in order to explain a repair method and a construction method to which the present invention is applied in relation to a repair method of a first embodiment.
FIG. 2 is a graph showing free energy generation temperature vs. oxygen pressure of oxide.
FIG. 3 is a cross-sectional view seen from a plane perpendicular to the construction direction in order to explain the construction method of overlay welding in the case of overlaying in multiple layers with respect to the repair method of the first embodiment.
FIG. 4 is a cross-sectional view seen from a plane perpendicular to the construction direction in order to explain the construction method of overlay welding in the case where the atmosphere is changed for overlaying with respect to the repair method of the first embodiment.
FIG. 5 is a cross-sectional view seen from a plane parallel to the construction direction in order to explain a repair method in water and a construction method to which the present invention is applied in relation to the repair method of the second embodiment.
FIG. 6 is a cross-sectional view seen from a plane perpendicular to the construction direction in order to explain a construction method for improving the corrosion resistance by surface melting of a sensitized metal material with respect to the repair method of the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Metal material, 102 ... Crack-like defect, 103, 104 ... Overlay metal, 105 ... Sensitized metal material, 106 ... Molten solidified layer, 201 ... Laser oscillator, 202 ... Laser beam, 203 ... Optical fiber, 204 ... Torch 205 ... Nozzle, 206 ... Inert gas / oxygen mixed gas, 207 ... Filler wire.

Claims

In the repair method of covering the surface of crack-like defects generated on the surface of the structure, including inclusions such as water and oxide inside, with the overlay metal formed by overlay welding using the laser as the welding heat source,
A method for repairing a crack-like defect , wherein the build-up welding is performed in an atmosphere in which a partial pressure of oxygen mixed with an inert gas is controlled, and the oxygen partial pressure is controlled according to a welding heat input .

A repair method for coating the surface of a region of a structure that has crack-like defects including inclusions such as water and oxide inside with a melt-solidified layer formed by surface melting using a laser as a welding heat source In
A method for repairing crack-like defects, wherein the surface melting treatment is performed in an atmosphere in which a partial pressure of oxygen mixed with an inert gas is controlled, and the oxygen partial pressure is controlled according to a welding heat input .

3. The method for repairing a crack-like defect according to claim 1, wherein the welding heat input is determined on the basis of a place where the opening width of the crack-like defect is widest. Repair method.

In the repair method of covering the surface of crack-like defects generated on the surface of the structure, including inclusions such as water and oxide inside, with the overlay metal formed by overlay welding using the laser as the welding heat source,
A method for repairing a crack-like defect, wherein the build-up welding is performed in an atmosphere in which a partial pressure of oxygen mixed with an inert gas is controlled, and the oxygen partial pressure is controlled according to the type of the inclusion .

A repair method for coating the surface of a region of a structure that has crack-like defects including inclusions such as water and oxide inside with a melt-solidified layer formed by surface melting using a laser as a welding heat source In
A repair method for a crack-like defect, wherein the surface melting treatment is performed in an atmosphere in which a partial pressure of oxygen mixed with an inert gas is controlled, and the oxygen partial pressure is controlled according to the type of the inclusion .

The method for repairing a crack-like defect according to any one of claims 1 to 5, wherein the repair is performed in an underwater environment while locally removing the water in the defect portion. Repair method.

The method for repairing a crack-like defect according to any one of claims 1 to 6, wherein a coating in an atmosphere in which an inert gas is mixed with oxygen is stacked in multiple layers.

The method for repairing a crack-like defect according to any one of claims 1 to 7, wherein the coating is performed in an atmosphere in which an inert gas is mixed with oxygen, and the coating is performed a plurality of times so as to cover the coated portion. A method for repairing a crack-like defect, characterized by coating under an active gas atmosphere or an atmosphere having a reducing property.